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The 41Ca(n,&agr;)38Ar reaction cross section was studied at the linear accelerator GELINA of the Institute for Reference Materials and Measurements in Geel (Belgium) and was determined up to a neutron energy of about 80 keV using the time-of-flight technique. In this energy region, 15 resonances were observed, whereas none were identified before. For some of them, resonance parameters such as resonance energy, total width, area, and spin could be determined. From the obtained cross-section data, Maxwellian averaged cross sections have been calculated at various stellar temperatures for further use in stellar models. [ABSTRACT FROM AUTHOR]

Abstract: The emission probabilities and the energy distributions of tritons, α and 6He particles emitted in the spontaneous ternary fission (zero excitation energy) of 250Cf and 252Cf and in the cold neutron induced fission (excitation energy ) of 249Cf and 251Cf are determined. The particle identification was done with suited telescope detectors, at the IRMM (Geel, Belgium) for the spontaneous fission and at the ILL (Grenoble, France) for the neutron induced fission measurements. Hence particle emission characteristics of the fissioning systems 250Cf and 252Cf are obtained at zero and at about 6.5 MeV excitation energies. While the triton emission probability is hardly influenced by the excitation energy, the 4He and 6He emission probability in spontaneous fission is higher than for neutron induced fission. This can be explained by the strong influence of the cluster preformation probability on the ternary particle emission probability. [Copyright &y& Elsevier]

This paper reports on the results of measurements of the (n,p) and (n,α) reactions on 26Al and 36Cl, in the neutron energy region up to 140 keV and 350 keV, respectively. The experiments were carried out at the GELINA neutron facility of the IRMM (Geel, Belgium). For both reactions several resonances could be identified which were never observed before. Using the obtained cross section data, reaction rates were calculated and compared with other experimental and theoretical values. [Copyright &y& Elsevier]

Charged particles emitted in ternary fission appear to have a Gaussian-shaped energy distribution, except for the α particles, for which mostly an important non-Gaussian low-energy tailing is reported. We realised good experimental conditions for studying the 235U(nth, f) ternary α energy distribution at the reactor of the ILL in Grenoble. Thanks to an intense and clean neutron beam, a small, thin sample of highly enriched U could be used, with an activity of only 1.6 Bq, so the measurements could be done without absorber in between the sample and the detector. With the resulting low detection limit of 6 MeV, a clearly asymmetric energy distribution was obtained, deviating by 6% from a Gaussian shape. This energy distribution has been deconvoluted into components corresponding to “true” ternary α''s and α''s originating from the decay of 5He particles. Ternary α emission yield data have been re-evaluated accordingly. [Copyright &y& Elsevier]

The 39Ar(nth,α)36S reaction has been studied for the first time. A sample containing 2.85×1014 39Ar atoms was produced at the ISOLDE facility at CERN. The number of 39Ar atoms in the layer was determined by measuring the 39Ar β-activity using a primary standardisation method. Subsequently, the sample was irradiated with thermal neutrons at the High Flux Reactor of the Institut Laue–Langevin. An upper limit of 0.29b was obtained for the 39Ar(nth,α)36S reaction cross-section. [Copyright &y& Elsevier]

Suitable 17O samples are required for the study of the 17O(n,α)14C reaction with various detectors. The electrospraying of metal oxides enriched in 17O onto an Al substrate yielded negative results: no 17O(nth,α) reactions were observed when irradiating these samples with thermal neutrons. These tests demonstrated the need to minimize the 10B content in sample and backing, since the 10B(nth,α1) reaction causes a strongly disturbing background. Good results were obtained in the reactor experiments using gaseous samples (17O enrichments of 58.2%, 72.1% and 85.5%) with a dedicated experimental setup. The experimental conditions being quite different at accelerators, an alternative method was developed to prepare samples suited for use in ionization chambers. For this purpose, 17O ions were implanted in ultra-pure Al foils. The thickest sample prepared in this way contains 8×1018 atoms of 17O, with a 10B/17O ratio of 10−4. [Copyright &y& Elsevier]

The ( th, α) reaction spectroscopy was done onzn andSe at the 87 m curved thermal neutron guide of the Grenoble high flux reactor. In each of theZn( n, α) Ni and Ni(n, α)Ni reactions, one line showed up corresponding to an α-particle transition to the first excited state inNi andNi with σ=11±3 μb and 159±20 μb respectively. In the case of the radioactiveZn( T=244 d) nucleus, two lines showed up corresponding to the ground state and the first excited state transitions inNi with large values of σ=1.0±0.1 b and σ=1.0±0.1 b. For theSe( n, α)Ge reaction, the ground state and first excited transitions were present with σ=940±20 μb and σ = 30±5 μb respectively. The spin-parity ( J) of the neutron resonance contributing at thermal energy are discussed. [ABSTRACT FROM AUTHOR]

The ( n, α) reaction onHf,Ta andBi was studied at the thermal neutron guide of the Grenoble high flux reactor. Upper limits of σ≦13μb, ≦μb and ≦0.3μb, respectively, were obtained for the a branches to the ground states in contrast to the values of ≈100μb to ≈500 mb reported in the literature. Possible reasons for these discrepancies are discussed. Furthermore, the present upper limits of the cross sections are compared with the values calculated from the statistical model. [ABSTRACT FROM AUTHOR]